This invention relates to welding and is concerned more particularly, but not exclusively, with automatic welding of annular components.
Production of satisfactory welds, particularly as section thickness increases, presents substantial problems in the art of welding, a major one of which is the adequate provision of suitable access for welding to the weld deposit area. In general, the access problem when producing such welds has been overcome by using components so shaped that, when brought together for welding, a "U" or "V" shaped preparation or channel of substantial included angle and/or width is presented for the deposition of weld material. One process of welding which is applicable to such formations is submerged arc welding, where several adjacent runs of weld metal are required to complete each layer. However, when the wider parts of the "U" or "V" are reached, the resulting large volumes of weld metal can prove disadvantageous in terms of long welding times, excessive coats and gross distortion on cooling. A further acute problem is posed when a welding torch is required to operate in other than a "downhand", that is to say, gravity welding, position, such as occurs in the automatic welding of a non-rotating pipe joint.
The prime object of the present invention is to provide portable apparatus for the automatic welding of narrow-gap weld preparations made between annular components.
The invention consists in welding apparatus for inert gas shielded arc welding comprising a welding gun for holding and controlling a non-consumable electrode and including means for supplying inert gas to the welding arc region by way of a gas cup surrounding but spaced from such an electrode when positioned in the gun, the welding gun being further provided with an extended gas shielding wall arrangement protruding for a substantial distance beyond the gas cup and capable, either by itself or in combination with a narrow gap weld preparation, of substantially enclosing an electrode in the gun, except for its tip, when the electrode is protruding for a similar distance beyond the gas cup.
With apparatus according to the invention, welding of annular components can be carried out with the apparatus stationary and the components rotating, or alternatively, with the components stationary in any convenient orientation and with the welding apparatus automatically orbitting the components.
In the preferred form of the invention the shielding wall arrangement comprises two elongate shields diametrically opposed on opposite sides of the general electrode axis position, while leaving intermediate opposed areas between longitudinal edges of the shields beyond the gas cup unenclosed, the arrangement being such as to provide effective gas shielding about an electrode in the welding torch when the electrode protrudes substantially beyond the gas cup. The apparatus may thus be applied to narrow gap weld preparations with the shielding arrangement so positioned that the two shielding walls in combination with the opposing walls of the preparation result in the electrode being substantially surrounded over its length from the gas cup to the tip region and giving effective inert gas shielding for welding.
Preferably the groove width W of the weld preparation has the relationship to the electrode diameter D of W = 11/2 D to 4D.
The shielding walls are preferably formed from stainless steel.
The invention further consists in a method of producing welds using welding apparatus in accordance with any of the preceding three paragraphs, and comprising the following steps:
(i) shaping the end walls of the members to be welded prior to welding to provide a narrow gap weld preparation of width less than that of the welding gun gas cup; PA1 (ii) arranging the electrode so as to protrude beyond the end of the shielding wall arrangement remote from the gas cup; PA1 (iii) inserting the extended shielding wall arrangement and electrode of the welding gun into the narrow gap weld preparation, to allow the electrode tip to be brought into close proximity to the root of the narrow gap weld preparation, while the gas cap of the gun is outside the narrow gap weld preparation; PA1 (iv) further inserting a weld filler wire into the narrow gap weld preparation so that its end may be fed into the arc gap region between the non-consumable electrode tip and the surface of the weld; and PA1 (v) proceeding to effect the weld by supplying electric current between the electrode and the root of the narrow gap weld preparation, and effecting relative movement between the electrode tip and the narrow gap weld preparation to deposit weld metal from the filler wire into the narrow gap weld preparation in the conventional way, but by means of only a single pass for each weld layer, at all depths of the weld.
The invention also consists in a method in accordance with the preceding paragraph in which the welding technique employed makes use of a pulsed current supply to the welding arc to ensure complete control of the weld pool of fusion at all times and in all welding positions.